The technology presented herein relates to a light-emitting device, a planar light source, and a liquid crystal display device.
LEDs (light-emitting diodes) have been widely used along with the improvement in their efficiency in recent years as a more energy-saving light source than electric bulbs and fluorescent lamps. In recent years, development of blue LEDs has been making progress, and white LEDs achieved by using a combination of a blue LED and a fluorescent material are also in practical use. White LEDs are being used as a light source for the small liquid crystal backlight devices of mobile terminals and the like. In particular, a liquid crystal backlight device using a side light-emitting type light-emitting device is being developed to achieve slimming down of mobile terminals and the like. A side light-emitting type light-emitting device applied to a liquid crystal backlight device is configured to be opposed to the end face of a light guide plate that is disposed on the back face of a liquid crystal panel, and introduce light into the light guide plate from the end face. In this case, a planar light source for a liquid crystal backlight device is constituted by a side light-emitting type light-emitting device, a light guide plate, and a mounting substrate on which the light-emitting device is mounted.
Since the side light-emitting type light-emitting device described above has an advantage that a liquid crystal backlight device can be slimmed down, such a side light-emitting type light-emitting device has also been gradually utilized in, for instance, a medium-sized liquid crystal backlight device of a notebook computer and the like, and a large-sized liquid crystal backlight device of a liquid crystal television and the like, recently. However, a higher-intensity light source becomes necessary with an increase in the size of a liquid crystal backlight device. Furthermore, it is also necessary to satisfy the demand for cost reduction compared to current light sources such as fluorescent tubes.
Here, although it is possible to consider using many LEDs as a technique for increasing the intensity of a light source, it will be difficult to satisfy the demand for cost reduction with this technique. Accordingly, it is necessary to increase the intensity by improving the performance of individual LEDs. It is possible to consider increasing the driving current for LEDs as a technique for increasing the intensity of individual LEDs. However, with this technique, improvement of heat dissipation properties and heat resistance properties of a light-emitting device (LED package) will be important due to an increase in the amount of heat generated by an LED.
Japanese Patent No. 3972889 (hereinafter, referred to as Patent Document 1) discloses a light-emitting device that improves light extraction efficiency by reflecting light from an LED chip by an inner wall face of a package. Further, Patent Document 1 discloses that in order to reflect light from the LED chip efficiently, white pigments such as titanium oxide are mixed in a resin that is used as the molding material of the package, and the package is formed using an insert molding method. JP 2005-159311A (hereinafter, referred to as Patent Document 2) discloses a light-emitting device whose package is a ceramic package.
However, a resin package as disclosed in Patent Document 1 has a problem that such a resin package cannot handle an increase in the size of a liquid crystal backlight device since its heat dissipation properties and heat resistance properties are insufficient. Further, a ceramic package as disclosed in Patent Document 2 has a problem that although such a ceramic package has higher heat conductivity compared to the resin package, it cannot be said that its heat dissipation properties are sufficient.
The present technology has been conceived in light of the above problems, and a feature thereof is to provide a light-emitting device that can improve heat dissipation properties, a planar light source including this light-emitting device, and a liquid crystal display device including this planar light source.
According to the present technology, means for solving the above problems are configured as follows.
A light-emitting device according to the example embodiments presented herein includes a light-emitting element, and a package substrate on which the light-emitting element is placed. The package substrate includes a placement face on which the light-emitting element is placed, a back face that is opposed to the placement face, and a mounting face that is opposed, between the placement face and the back face, to a mounting substrate when the light-emitting device is mounted, and includes a first recess portion that extends, on the mounting face, from the back face toward the placement face and that has a first heat conduction member formed on a surface thereof, and an intermediate heat conduction member for conducting heat between the light-emitting element and the first heat conduction member.
According to the above configuration, as a heat dissipation path for releasing heat generated by the light-emitting element toward the mounting substrate, a heat dissipation path including the first heat conduction member that is opposed to the mounting substrate, and the intermediate heat conduction member for conducting heat between the light-emitting element and the first heat conduction member is formed. Thereby, heat generated by the light-emitting element can be efficiently released toward the mounting substrate, and thus heat dissipation properties of the light-emitting device can be improved. Further, since the space that can be filled with a fixing wax material with which the package substrate is fixed to the mounting substrate can be secured, the parallelism of the mounting face relative to the mounting substrate can be secured. Further, when the light-emitting device (the mounting face) is mounted on the mounting substrate, light can be emitted in the side face direction.
Further, in the light-emitting device according to the present embodiments, the intermediate heat conduction member includes a second heat conduction member that is connected to the first heat conduction member and extends toward the light-emitting element inside the package substrate.
According to the above configuration, as a heat dissipation path for releasing heat generated by the light-emitting element toward the mounting substrate, a heat dissipation path including the second heat conduction member that is connected to the first heat conduction member and extends toward the light-emitting element inside the package substrate, and the first heat conduction member that is connected to the second heat conduction member is formed. Thereby, heat generated by the light-emitting element can be efficiently released toward the mounting substrate, and thus heat dissipation properties of the light-emitting device can be improved.
Further, the light-emitting device according to the present embodiments includes a placement heat conduction member on which the light-emitting element is placed, and the placement heat conduction member is connected to the second heat conduction member.
According to the above configuration, as a heat dissipation path for releasing heat generated by the light-emitting element toward the mounting substrate, a heat dissipation path including the placement heat conduction member on which the light-emitting element is placed, and the second heat conduction member that is connected to the placement heat conduction member is formed. Thereby, heat generated by the light-emitting element can be further more efficiently released toward the mounting substrate, and thus heat dissipation properties of the light-emitting device can be improved.
Further, in the light-emitting device according to the present embodiments, the placement heat conduction member and the second heat conduction member are formed integrally.
According to the above configuration, since the placement heat conduction member and the second heat conduction member can be formed integrally, heat conductivity can be improved, and the manufacturing process can be simplified.
Further, in the light-emitting device according to the present embodiments, the intermediate heat conduction member includes a third heat conduction member that is disposed from the placement face up to the back face inside the package substrate, and a fourth heat conduction member that connects the third heat conduction member and the first heat conduction member on the back face.
According to the above configuration, as a heat dissipation path for releasing heat generated by the light-emitting element toward the mounting substrate, a heat dissipation path including the third heat conduction member that is disposed from the placement face up to the back face inside the package substrate, the fourth heat conduction member that is disposed so as to connect the third heat conduction member and the first heat conduction member on the back face, and the first heat conduction member that is connected to the fourth heat conduction member is formed. Thereby, heat generated by the light-emitting element can be efficiently released toward the mounting substrate, and thus heat dissipation properties of the light-emitting device can be improved.
Further, the light-emitting device according to the present embodiments includes a placement heat conduction member on which the light-emitting element is placed, and the placement heat conduction member is connected to the third heat conduction member.
According to the above configuration, as a heat dissipation path for releasing heat generated by the light-emitting element toward the mounting substrate, a heat dissipation path including the placement heat conduction member on which the light-emitting element is placed, and the third heat conduction member that is connected to the placement heat conduction member is formed. Thereby, heat generated by the light-emitting element can be further more efficiently released toward the mounting substrate, and thus heat dissipation properties of the light-emitting device can be improved.
Further, in the light-emitting device according to the present embodiments, the placement heat conduction member and the third heat conduction member are formed integrally.
According to the above configuration, since the placement heat conduction member and the third heat conduction member can be formed integrally, heat conductivity can be improved, and the manufacturing process can be simplified.
Further, in the light-emitting device according to the present embodiments, the package substrate is a ceramic substrate.
According to the above configuration, since the package substrate is constituted by a ceramic substrate, heat resistance properties can be improved, and reliability can be improved.
Further, in the light-emitting device according to the present embodiments, the first recess portion is formed from the back face side of the mounting face to a position corresponding to the placement face.
According to the above configuration, a flat face can be secured on the mounting face, and thus the accuracy of mounting on the mounting substrate can be secured.
Further, in the light-emitting device according to the present embodiments, a wall face of the first recess portion is formed so as to have an arc-shaped cross section.
According to the above configuration, the first recess portion can be easily formed.
Further, the light-emitting device according to the present embodiments includes an internal anode terminal and an internal cathode terminal that are connected to the light-emitting element. The internal anode terminal is connected to an external anode terminal that is provided on the mounting face, and the internal cathode terminal is connected to an external cathode terminal that is provided on the mounting face.
According to the above configuration, the internal anode terminal and the internal cathode terminal can be connected to wiring of the mounting substrate via the external anode terminal and the external cathode terminal.
Further, in the light-emitting device according to the present embodiments, the internal anode terminal and the internal cathode terminal each extend in a direction parallel to the placement face on which the light-emitting element is placed.
According to the above configuration, the package substrate can be easily formed.
Further, in the light-emitting device according to the present embodiments, the external anode terminal and the external cathode terminal are each provided from an end on the back face side of the mounting face to a position corresponding to the placement face.
According to the above configuration, the accuracy with which the external anode terminal and the external cathode terminal are connected to the wiring of the mounting substrate can be improved, and the reliability of connection can be secured.
Further, in the light-emitting device according to the present embodiments, the external anode terminal and the external cathode terminal are respectively provided on second recess portions that are formed in corner portions of the package substrate.
According to the above configuration, the external anode terminal and the external cathode terminal can be easily connected to and aligned with the wiring of the mounting substrate.
Further, in the light-emitting device according to the present embodiments, a wall face of each of the second recess portions is formed so as to have an arc-shaped cross section.
According to the above configuration, the second recess portion can be easily formed.
Further, in the light-emitting device according to the present embodiments, a difference in level is provided between the placement face on which the light-emitting element is placed and an internal terminal plane that is constituted by the internal anode terminal and the internal cathode terminal.
According to the above configuration, it is possible to easily prevent the internal anode terminal and the internal cathode terminal from short-circuiting.
Further, in the light-emitting device according to the present embodiments, the internal terminal plane is disposed closer to the back face than the placement face on which the light-emitting element is placed is.
According to the above configuration, the package substrate can be easily formed.
A planar light source according to the present embodiments includes the light-emitting device according to the present invention, a mounting substrate on which the light-emitting device is mounted, and a light guide plate for guiding light from the light-emitting device. The first recess portion is filled with a wax material for fixing the package substrate to the mounting substrate.
According to the above configuration, as a heat dissipation path for releasing heat toward the mounting substrate, a heat dissipation path for releasing heat toward the mounting substrate via the wax material is constituted, and thus heat dissipation properties can be improved. Further, since the first recess portion is filled with the wax material, positioning of the mounting face relative to the mounting substrate is performed with high accuracy, and thus the uniformity of light that exits from the light guide plate can be improved.
A planar light source according to the present embodiments includes the light-emitting device according to the present invention, a mounting substrate on which the light-emitting device is mounted, and a light guide plate for guiding light from the light-emitting device. Each of the second recess portions is filled with a wax material for fixing the package substrate to the mounting substrate.
According to the above configuration, as a heat dissipation path for releasing heat toward the mounting substrate, a heat dissipation path for releasing heat toward the mounting substrate via the wax material is constituted, and thus heat dissipation properties can be improved. Further, since each of the second recess portions is filled with the wax material, positioning of the mounting face relative to the mounting substrate is performed with high accuracy, and thus the uniformity of light that exits from the light guide plate can be improved.
A liquid crystal display device according to the present embodiments includes the planar light source according to the present embodiments, and a liquid crystal panel, and the planar light source is used as a backlight of the liquid crystal panel.
According to the above configuration, since the planar light source having good heat dissipation properties and excellent light uniformity is used as a backlight, the liquid crystal display device that can perform uniform display with high accuracy can be achieved.